added base_path;

--- a/src/Pure/Thy/browser_info.ML	Tue Jan 13 14:31:09 1998 +0100
+++ b/src/Pure/Thy/browser_info.ML	Tue Jan 13 18:03:37 1998 +0100
@@ -79,7 +79,7 @@
 sig
   val output_dir       : string ref
   val home_path        : string ref
-
+  val base_path        : string ref
   val make_graph       : bool ref
   val init_graph       : string -> unit
   val mk_graph         : string -> string -> unit